Magnetic hard disk drives (HDDs) have been employed in information technology as a low-cost means for providing random access to large quantities of data. Consequently, as digital technologies have greatly expanded the need for data storage in all aspects of modern life, areal density of information stored in HDDs has been continuously increased. However, there is a physical limitation for the minimum width of a write head when using conventional data recording techniques, such as perpendicular magnetic recording (PMR). This minimum width has prevented further decreases in written track width and areal density of HDDs, even though the width of a read head can be further reduced.
A recently developed technology that has further increased the areal density of magnetic HDDs is shingled magnetic recording (SMR). In an HDD that employs SMR, adjacent data tracks on a magnetic disk are each written (one group at a time) so as to overlap, and therefore overwrite, a portion of the previously written data track. As a result, the data tracks written in an SMR HDD are compressed in width to allow for increased data density in an HDD.
However, SMR HDDs have a significant drawback. Once a data track is written in a shingled structure, that data track cannot be updated in place because that would overwrite and destroy data in one or more adjacent and overlapping data tracks. That is, random block overwrites cannot be performed on shingled data tracks without disturbing existing data. To avoid re-writing an entire group of shingled data tracks each time a host requests an overwrite of data within that group of tracks, data associated with write requests are commonly stored in a so-called “media cache.” Typically, the media cache is located in a non-SMR region of the HDD, thereby allowing random block writes to the HDD. Such data stored in the media cache can be later written into the appropriate SMR region of the HDD along with other write data associated with that SMR region.
Unfortunately, a read request received by an SMR HDD that includes some data stored in the SMR region and some data stored in the media-cache region of the HDD can result in poor drive performance. For example, multiple portions of a document may be updated by the host, and therefore require writes to multiple data blocks associated with the document in the media cache of the HDD. Consequently, a subsequent read request by the host for the entire document will effectively be translated into multiple random read requests, as the drive repeatedly seeks between the SMR region and the media-cache region of a disk to read the most up-to-date data associated with the requested document.